The Effect of Temperature on Attenuation-Correction Schemes in Rain Using Polarization Propagation Differential Phase Shift

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  • 1 Applied Research Corporation, Landover, Maryland
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Abstract

Several investigators propose estimating the rates of attenuation using the difference in the phase with increasing distance between horizontally and vertically polarized microwaves. These attenuation estimates can then be used to correct measured radar reflectivity factors at horizontal and vertical polarizations and their ratio (differential reflectivity) for attenuation biases that may afflict polarization-based quantitative estimates of rainfall, even at frequencies as low as 3 GHz.

Unfortunately, although this polarization phase difference does not depend upon the temperature of the rain, the attenuation is dominated by temperature-sensitive molecular absorption for frequencies below about 9 GHz. Neglecting the effects of temperature when estimating attenuation from the polarization phase difference increases the fractional standard error only slightly at 9 GHz but significantly at 5 and 3 GHz Nevertheless, even though the fractional error is about two to three times larger at 5 and 3 GHz than at 9 GHz, the absolute error (the product of the fractional error and the attenuation) is still greater at higher frequencies. Consequently, in spite of increased sensitivity to temperature, attenuation corrections using polarization phase differences work best at lower frequencies.

Abstract

Several investigators propose estimating the rates of attenuation using the difference in the phase with increasing distance between horizontally and vertically polarized microwaves. These attenuation estimates can then be used to correct measured radar reflectivity factors at horizontal and vertical polarizations and their ratio (differential reflectivity) for attenuation biases that may afflict polarization-based quantitative estimates of rainfall, even at frequencies as low as 3 GHz.

Unfortunately, although this polarization phase difference does not depend upon the temperature of the rain, the attenuation is dominated by temperature-sensitive molecular absorption for frequencies below about 9 GHz. Neglecting the effects of temperature when estimating attenuation from the polarization phase difference increases the fractional standard error only slightly at 9 GHz but significantly at 5 and 3 GHz Nevertheless, even though the fractional error is about two to three times larger at 5 and 3 GHz than at 9 GHz, the absolute error (the product of the fractional error and the attenuation) is still greater at higher frequencies. Consequently, in spite of increased sensitivity to temperature, attenuation corrections using polarization phase differences work best at lower frequencies.

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